1. Field of the Invention
The present invention relates to separation of sheets in a sheet feeding device.
2. Description of the Related Art
A general image reading apparatus reads the image of a document placed on a document platen by using an optical unit provided under the document platen. Alternatively, a general image reading apparatus reads the image of a document conveyed from a document tray by an automatic document feeder (ADF) provided in the image reading apparatus.
In a document separation and feeding mechanism of an ADF, it is a common configuration to control a separation roller and a feeding roller by respective independent motors, or to control them by a single motor with a clutch connected. However, use of many motors and clutches results in an increase in apparatus size and in cost, so that various devices have been made in this connection.
For example, in U.S. Pat. No. 5,601,281, a document feeding device has a motor configured to make normal and reverse rotation, a first drive shaft configured to be driven at the time of normal rotation, and a second drive shaft configured to be driven at the time of reverse rotation. A separation roller is connected to the first drive shaft, and a registration roller (a feeding roller) is connected to the second drive shaft. The document feeding device performs separation and feeding conveyance by normal and reverse rotation of the motor. This helps to achieve a reduction in apparatus size and in cost.
In a separation/feeding mechanism in which switching between separation and feeding (pulling-out) is effected by a change in the rotational direction of a single motor, it is impossible to change the rotational direction of the motor until the trailing edge of a document passes through the feeding roller. Thus, it is impossible to separate the next document until the trailing edge of the document passes through the feeding roller and the motor stops, thus resulting in a rather long document feeding interval. As a result, the productivity in document reading is reduced.